Muzzle loading rifles have an essentially closed breech at the rear of the barrel, so that powder and bullets must be loaded at the muzzle or forward end of the barrel. A typical muzzle loading rifle has a barrel with a breech plug attached to occupy an enlarged rear bore portion of the barrel at the breech end. In some rifles, the breech plug is not meant to be removed. In others, the breech plug can be removed to facilitate cleaning of the breech plug and rifle bore.
Many different styles of breech plugs have been developed for muzzleloading firearms. A properly designed breech plug should seal the primer by having minimal tolerance between the primer seat and the breech face. The breech plug should also effectively facilitate efficient flow of the flame and gas through the flash hole by including a proper transition angle between the flash channel/fire channel to the flash hole. Failure to meet any or all of these requirements may cause poor ignition, inconsistent accuracy, or hangfires and misfires.
Prior art breech plugs are known to sometimes provide a loose fit when the primer is installed in the primer pocket. The looser the primer fit (circumferentially or longitudinally), the greater the blowback, which makes it less likely that sufficient flame and gas will flow from the primer to the powder. The loose fit results in a measurable loss of energy back through the primer pocket along the walls between the primer and the primer pocket walls. The rearwardly escaping gases leave excessive fouling in the breech area, and these gases can also exit the gun, causing damage to the scope and posing a danger to the shooter. Finally, a loose fitting primer can inconvenience the shooter by falling out of the primer pocket if the breech is open.
Therefore, there is a need for a muzzleloading firearm with a breech plug having a primer seal facility that effectively prevents or minimizes the flame and hot gases from the primer escaping rearward from the primer pocket.
Although prior art breech plugs are known to employ O-rings, those O-rings are typically circumferentially attached the breech plug in a manner to contain the high pressure of powder ignition to prevent fouling of breech plug threads. These prior art breech plug O-rings are either made of rubber or are metal gas check piston rings.
It is also known to place an O-ring into the primer hole against the primer seat at the front of the primer such that when the breech is closed, the primer is forced into the O-ring to create a better seal. However, the O-ring is not held in place within the breech plug when the primer is not present.